1. Field of the Invention
The present invention relates to systems for modeling penetrating brain injury (PBI) typically relating to ballistics. More particularly, the present invention relates to a fluid percussion system and method for simulating brain injuries in animal models.
2. Background Art
Penetrating brain injury (PBI) from projectiles is a leading cause of mortality and morbidity in modern warfare and accounts for a significant number of traumatic brain injuries worldwide. Therefore, the accurate simulation of ballistic PBIs in an animal model is important for clinical PBI pathology.
A conventional system for simulating ballistic brain injuries involves a closed hydraulic system actuated by a manually controlled pendulum to deliver a pulsed fluid for rapid inflation and deflation of a balloon (representing the penetrating device) that is inserted in an animal test subject. A hydraulic cylinder/piston assembly may include a striker plate at an exposed end of the piston that is hit by a falling pendulum, whereby high pressure fluid is delivered from the cylinder through a high pressure hose. The hose is hydraulically connected to the balloon inside the test subject (e.g., inside a brain of a rat) that becomes inflated during the duration for the pressure pulse. The balloon may be fixed in position and connected to the hose by means of a chronically implanted Luer lock fitting on the rat's skull.
By changing the angle through which the pendulum falls or by adding weight to the pendulum, the striking force of the pendulum on the striker plate of the hydraulic cylinder/piston assembly may be adjusted. A pressure transducer coupled to an oscilloscope may measure the system pressure. A magnet may be mounted on the pendulum and a magnetic switch may be mounted near the striker plate. When the magnet on the pendulum swings past the magnetic switch, a trigger switch for the oscilloscope may be activated, whereby the pressure data can be matched with pulse time and a timebase of the oscilloscope may be provided. For a flat faced striker plate, a time duration of the pulse may be about 10 ms, which may be lengthened by attaching a facing of shock absorbing foam to the striker plate. Model #HPD-1700 Fluid Percussion Device, produced by Dragonfly, R&D, Inc. of Ridgeley, W. Va., is an example of a conventional, pendulum-based fluid percussion device for simulating ballistic brain injuries. The Model #HPD-1700 Installation and Setup Manual, available at www.dragonflyinc.com/FP/HPD1700.htm, is incorporated herein in its entirety by reference thereto.
It is necessary to gauge the size of the inflated balloon (i.e., balloon diameter) to measure and quantify the extent of the resulting brain lesion, as well as allow calibration of the system (i.e., balloon size control). Typically, such a calibration of balloon size involves a ruler placed adjacent the balloon whose inflation is videotaped. The video-recorded balloon inflation may then be frozen at a video frame in which the balloon is perceived to be at its maximum diameter frame, thereby permitting visual measurement on the ruler of the balloon size. Such a method of calibration involves the operator to determine at which frame the balloon is at its maximum diameter and to compare the balloon size against the ruler.
This conventional system for PBI modeling has several limitations. The manual operation of pendulum provides inconsistent pulses and increases experimental variability in the PBI modeling studies. Such a system is also unable to perform rapid and consecutive pulses, and data capture may be difficult when the output reading is oscilloscope-based. Further, it is difficult to adjust the time duration of the pulse and striking force of the pendulum. In addition, the calibration method for gauging balloon size is not only difficult, but also involves increased likelihood of human error in the determination of balloon size. This error may lead to inaccurate determination of balloon inflation size and irreproducible experiments during PBI studies.
What is needed, therefore, is a fluid percussion system and method for modeling PBI in which pulse and duration are easily adjusted, consistent multiple pulses may be delivered to the animal test subject, and reproducible and quantifiable measures of outcome are generated. The present invention satisfies these and other needs, as will be made apparent by the description of the present invention that follows.